Studies in search of a suitable experimental insect model for xenodiagnosis of hosts with Chagas' disease: 4 - The reflection of parasite stock in the responsiveness of different vector species to chronic infection with different Trypanosoma cruzi stocks Estudos em busca de um inseto modelo para o xenodiagnóstico em hospedeiros com doença de Chagas: 4 - O reflexo da cepa do parasito na resposta de diferentes espécies vetoras à infecção crônica com diferentes isolados do Trypanosoma cruzi

Previous studies (1982,1987) have emphasized the superiority of sylvatic vector species over domestic species as xenodiagnostic agents in testing hosts with acute or chronic infections by T. cruzi "Y" stock. The present study, which is unique in that it contains data on both infectivity rates produced by the same stock in 11 different vector species and also the reaction of the same vector species to seven different parasite stocks, establishes the general validity of linking efficiency of xenodiagnosis to the biotope of its agent. For example, infectivity rates produced by "São Felipe" stock varied from 82.5% to 98.3% in sylvatic vectors but decreased to 42.5% to 71.3% in domestic species. "Colombiana" stock produced in the same sylvatic vectors infectivity rates ranging from 12.5% to 45%. These shrank to 5%-22.5% in domestic bugs. The functional role of the biotope in the vector-parasite interaction has not been eluddated. But since this phenomenon has been observed to be stable and easy to reproduce, it leads us to believe that the results obtained are valid. Data presented also provide increasing evidence that the infectivity rates exhibited by bugs from xenodiagnosis in chronic hosts, are parasite stock specific. For example, infectivity rates produced by "Berenice", "Y", "FL" and "CL" varied in R. neglectus from 26.3% to 75%; in P. megistus from 56.3% to 83.8%; in T. sordida from 28.8% to 58.8% in T. pseudomaculata from 41.3% to 66.3% and in T. rubrovaria from 48.8% to 85%. Data from xenodiagnosis in the same hosts, carrying acute infections by the same parasite stocks, gave the five sylvatic vectors a positive rating of approximately 100%, thus suggesting that the heavy loads of parasites circulating in the acute hosts obscured the characteristic interspecific differences for the parasite stock. Nonetheless these latter were revealed in the same hosts with chronic infections stimulated by very low numbers of the same parasite stocks. Certain observations here described lead us to speculate as to the possibility of further results from other parasite stocks, allowing the association of the infectivity rates produced in bugs by different parasite stocks with the isoenzymic patterns revealed by these stocks.Estudos anteriores (1982,1987) enfatizaram a superioridade das espécies vetoras silvestres às domiciliadas, como agentes do xenodiagnóstico nas infecções agudas e crônicas pelo isolado Y do T.cruzi. Os dados atuais estabeleceram a generalidade deste fenômeno. Por exemplo, a proporção de positivos nas infecções por 'São Felipe" variou de 82,5% a 98,3% nos vetores silvestres, caindo para 42,5% a 71,3% em espécies domiciliadas. Ficou claro o envolvimento do isolado do T.cruzi na resposta do vetor à infecção crônica por T.cruzi. Por exemplo, os índices de infectividade produzidos por "Berenice", "Y", "FL" e "CL" variaram de 56,3% a 83,3% em P.megistus e de 28,3% a 58,8% em T.sordida. Sendo a resposta das mesmas espécies vetoras às infecções agudas pelos mesmos isolados altamente uniformes, aproximando-se a 100%, sugere-se que a grande carga parasitária nas infecções agudas oculta as diferenças interespecíficas existentes entre os isolados do T.cruzi. A análise dos dados obtidos levou a especular que resultados adicionais de mais isolados permitiriam associar os índices de infectividade, produzidos por diferentes isolados do T.cruzi, aos perfis isoenzimáticos revelados por esses.